Within each of these sites there lies a certain amount of peer pressure... sign up for this... link to that... forward this... comment there. One of the more visible trends/fads I've tried to avoid is the phenomenon of retweeting. Even though retweeting has become so much a practice that widgets exist to show how often a blog post has been redistributed and people are begging to "Please RT", we're saying no. We don't expect you to retweet our articles, and we won't be retweeting yours.
Given much of my own activity on Twitter is to distribute links to this site, or to highlight others' work, with the occasional comments replying to other Twitter users, we have a high level of linking over conversation. It's enough that some services, like Twanalyst, even call us "spammy", given our high link to retweet ratio.
Twanalyst says I am spammy and don't retweet
Twitter is a land where 140 characters is all you've got to express yourself. If you think you don't have enough interesting data to share 140 characters of your own, but instead need to piggyback on someone else's tweet, then maybe you should rethink why you're using the service.